Translator

09 February 2014

BOBGRAM

WEATHERGRAM
YOTREPS
Issued 09 February 2014
Bob McDavitt's ideas for sailing around the South Pacific.
Disclaimer: Weather is a mix of pattern and chaos; these ideas are from the
patterned world of weather maps, so please fine-tune to your place.
Dates are in UTC unless otherwise stated.

SOI The Southern Oscillation Index SOI sums up the weather pattern over the
South Pacific as one number. It is based on the standardized difference in
the barometer readings between Tahiti and Darwin.
SOI (30 day running mean) has jumped into possible La Nina territory over
the past few weeks. Its 30-day running mean has remained over plus 1.30 from
1 to 9 Feb if this continues for a few more weeks then we will be diving
onto a new La Nina episode.

The Ocean: The warmer the sea the quicker it evaporates, tossing water
vapour into the air, where is rises and cools into cloud. The equatorial
Pacific region hosts the widest and warmest sea on the planet. Thus its sea
surface temperatures SST may be thought of as a factor in the running of
planetary weather engine. When SST in the target zone (equatorial Pacific
between dateline and Galapagos) are notably cooler than normal , this is
called a La Nina episode.
The SST in the target zone is measured by the NINO3.4 index and this has
taken a notable drive during the past few weeks. This means that both
atmospheric and oceanic parameters in the tropical Pacific are now trending
towards a La Nina event.

Interesting websites
A few weeks ago I mentioned the great imagery available at http://earth.
nullschool.net/Well, they have now added latest imagery from the OSCAR satellite and these
are worth checking out- (click on earth then Mode>Ocean). A quick link
covering the Tasman Sea is at bit.ly/1aFdDNm and sort of explains why the
larger snapper are offshore from Auckland at present (thanks to John Neal of
MAHINA TIARE III for this update).

TROPICAL TOPICS
The risk of tropical cyclone formation in the South Pacific is expected to
be LESS than normal over the next few weeks.
Cyclones made brief appearances over western New Caledonia (EDNA) and in
Gulf of Carpentaria (FLETCHER) last week. At present TC FOBANE is in the
south Indian Ocean.

The Australia Monsoonal trough is still in peak heat and wet the wet zone is
draping northern Australia and the hot zone is covering central and southern
Australia. The Monsoonal Low currently over NW Australia is expected to soon
start travelling south and the southeast across central Australia this week
spawning a series of smaller lows all going southeast and moving into the
South Tasman Sea by the weekend 15/16 Feb and then across southern NZ early
next week. These lows are likely to have very strong wind changes with them
and the Monsoonal trough is bringing a culmination of heat-wave conditions
to central and then SE Australia over the next few days. Peak days may be
Tue /Thu 11/13 Feb
see www.bom.gov.au/australia/heatwave/

WEATHER ZONES
South Pacific Convergence Zone SPCZ
EDNA took the main part of the convection that was in the Coral Sea away
into the mid-latitudes. What remains behind may need/take few weeks to
rebuild.
There is a second branch of the SPCZ between Samoa and French Polynesia,
with random and moderate activity. There is a tropical low between Southern
Cooks and Papeete tonight with gale force squalls and lots of lightning. It
is expected to go south and then fade mid-week near 25S.

Sub-tropical Ridge STR
A HIGH is expected to get pushed out of the way by the advancing Australian
monsoonal trough on Tuesday/Wednesday and then travel NE across the Tasman
Sea on Thursday and across the North Island on Friday/Saturday/Sunday-
cicada weather.

New Zealand area
NZ starts the week with a ridge over the south and a trough to the NE. A
passing small but intense Southern Ocean Low is expected to cross the South
Island on Tuesday and Wednesday followed by a cool SW flow covering all NZ
by Thursday 13th.
Then that high should cross NZ late in the week followed by hot northerly/NW
winds for the South island on Sat/Sun 15/16 Feb.